Abstract: Long-term comparative effectiveness of the Lap Band Surgery for morbid obesity has grown exponentially and is now the 2nd most common abdominal operation in the United States. A large part of the growth has been driven by the dramatic increase in the use of laparoscopic adjustable gastric banding (Lap Band). However, there are growing concerns about the longer term safety and effectiveness of the Lap Band. There is emerging evidence of high rates (up to 30% in some case series) of late complications, including band erosion and slippage. Moreover, many are concerned because the Lap Band has not been as effective, in terms of weight loss and comorbid disease resolution, in the real world as compared to early trials. Finally, whether there is heterogeneity in safety and effectiveness, either across patient subgroups or provider characteristics, has not been rigorously assessed. A recent policy change by the Center for Medicare and Medicaid Services (CMS), the 2006 national coverage decision for bariatric surgery, provides a unique natural experiment for evaluating the long-term comparative effectiveness of the Lap Band. The change in practice can be used as an instrumental variable to mitigate selection bias in comparing the Lap Band vs. laparoscopic gastric bypass, the gold-standard weight loss procedure. We have the following three Specific Aims: Aim 1. To evaluate the comparative long-term safety of the Lap Band in Medicare patients. Using the national Medicare population, we will evaluate the long term safety of the Lap Band compared to laparoscopic gastric bypass surgery. Specifically, we will evaluate 90-day, 1-year, and 5-year reoperation and hospitalization rates for complications of the initial surgery. Aim 2. To evaluate the comparative long-term effectiveness of the Lap Band in Medicare patients. Using the national Medicare population, we will evaluate the impact of the Lap Band on healthcare services and related Medicare payments for obesity-related comorbid conditions. Aim 3. To evaluate heterogeneity in the safety and effectiveness of the Lap Band in Medicare patients. Because the Lap Band may be more or less beneficial for different subgroups, we will evaluate its effectiveness, in terms of safety and effectiveness, for patients with different age, baseline health status, and select comorbid diseases. We will evaluate heterogeneity in the effectiveness of the Lap Band across different provider characteristics (e.g., hospitals and surgeons with more vs. less experience or volume). Results from this study will most immediately impact the Center for Medicare and Medicaid Services (CMS) and their national coverage decision for bariatric surgery. CMS actively re-evaluates bariatric coverage and accurate estimates of real- world safety and effectiveness of Lap Band compared to other procedures will help their evidence-based coverage decisions. Patients will be the ultimate beneficiaries of this research as they will be better informed regarding the true long term risks and benefits of the Lap Band.